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Oct. 29, 1963 E. D. CROSS MASK FOR FACSIMILE SCANNER 3 Sheets-Sheet 1Original Filed Aug. 27, 1953 INVENTOR EDWARD D. CROSS BY w [a WNWququqmmw ATTORNEY Oct. 29, 1963 E. D. @2055 Re. 25,468

MASK FOR FACSIMILE SCANNER Original Filed Aug. 27, 1953 3 SheetsFSheet 2INVENTOR E= E EDWARD D. CROSS ATTORNEY Oct. 29, 1963 E. D. cRoss Re. 25,

MASK FOR FACSIMILE SCANNER Original Filed Aug. 27, 1953 3 ee s-Sheet 3INVENT OR EDWARD D. CROSS BY w 124;) ATI'ORNEY United States Patent 125,468 MASK FOR FACSIMILE SCANNER Edward D. Cross, Brockton, Mass,assignor to Alden Research Foundation, Westboro, Mass, a Massachusettsbusiness trust Original No. 2,929,871, dated Mar. 22, 1960, Ser. No.376,834, Aug. 27, 1953. Application for reissue July 14, 1951, Ser. No.127,438

3 Claims. (Cl. 178-7.1)

Matter enclosed in heavy brackets appears in the original patent butforms no part of this reissue specification; rnatter printed in italicsindicates the additions made by reissue.

In facsimile scanners such as the type wherein transverse elements ofthe copy are successively scanned as they are moved adjacent anelongated slot, the light reaching the photoelectric cell from the edgesof a copy having a uniform density is materially less than that receivedfrom the central portions. This phenomenon apparently is caused byseveral factors including among others the reduction in the amount oflight falling on the lens system from the end portions of the slotbecause of the greater angle of incidence, of the light rays on thesurface of the lens system, the longer light path, the reduced output ofthe ends of the elongated electric lamps illuminating the slot whichfurther decreases with age, the thickness of the material forming thehelical aperture and the non-linearity of response of the lightsensitive electrode of the photoelectric cell. The net result of thesefactors is a non-uniform electrical output from the photoelectric cellwhich is undesirable because of the variations in contrast in therecord.

It is accordingly the principal objects of this invention to providemeans which improves the output characteristics of a facsimile scanner;which provides com pensation so that the electrical output is constantfor copy of uniform density, which is simple and economical toconstruct, which can be incorporated in existing scanners, which has nomoving parts, which is readily adjustable, and which advances thefacsimile art generally.

These and other objects will be apparent from the following descriptionof a specific embodiment of the invention which refers to drawingswherein:

FIG. 1 is a plan view of a mask for an optical facsimile scanner;

FIG. 2 is a side elevation view with portions broken away;

FIG. 3 is a fragmentary side elevation view of scanner having a portionof the side wall broken away to show the position of the mask;

FIG. 4 is a schematic view showing the path of the light rays in thescanner shown in FIG. 3; 7

FIGS. 5 and 6 are sectional views on line 5-5 and 66 respectively ofFIG. 4 when no mask is used;

FIG. 7 is a voltage time diagram of the output of the scanner without amask;

FIG. 8 is a similar diagram when a mask is used in the scanner; and

FIGS. 9 and 10 are sectional views taken on lines S5 and 6-6 of FIG. 4when a mask is used.

A scanner 10 only the upper portion of which is illustrated in FIG. 3 isof the type wherein the copy is fed by a transverse slot 12 in a table14 by feeding means such as rolls which form no part of the presentinvention and are not shown. The transverse elements of the copy exposedat the slot 12 are brightly illuminated by two elongated tubular lampsdesignated generally at 16 so that light rays are reflected from thecopy and directed by the lens system L to impinge upon a photoelectriccell (not shown). Scanning is obtained by the relative movement oflinear and helical optical apertures, such as is illustrated in patentapplication Ser. No. 240,418,

"ice

filed August 4, 1951, wherein the above discussed elements are all shownand described in detail.

It has been found that with the above scanner if copy consisting ofalternate black and white bands such as is shown at C (FIG. 4) is fedlengthwise of the bands so that an effective elemental scanning area,such as the scanning spot S, moves transversely thereto, the electricaloutput of the photocell for one complete scaning movement lengthwise ofthe slot 12 varies according to the voltage-time diagram of FIG. 7forming a trace such as would be recorded by an oscillograph. It will benoted that with a copy having an alternate band of black and white witha uniform contrast therebetween the average signal strength increasesfrom a minimum at the beginning of the scanning stroke at one end of theslot 12 (FIG. 3) to a maximum in corresponding to the center portions ofthe slot and then again decreases to a minimum at the other end of theslot.

The peaks 2 at either end of the diagram are caused by the synchronizingor framing pulses of the scanner. Although as discussed heretofore anumber of factors are apparently involved in this phenomenon one of theprincipal factors appears to be the reduction of light trans ferred tothe photoelectric cell by lens system L from the scanning spot S when itis near the ends of the slot as compared with the light when the spot isnear the center, as can clearly be seen by comparing the areas of thecross sections of the light beams b1 and b2 (FIGS. 5 and 6) taken inplanes normal to the axis of the lens system.

To regulate the amount of light impinging upon the photoelectric cellfor similar copy irrespective of the instantaneous position of thescanning spot S, I interpose a mask 20 between the slot 12 and the lenssystem L as is shown in FIG. 3. As is best illustrated in FIGS. 1 and 2the mask comprises a diaphragm formed of a plurality of fingers 22 whichare supported between two horizontally spaced plates 24. Alternatefingers 22 are arranged respectively in two parallel planes whicharrangement permits the edges of each finger to overlap the edges ofadjacent fingers without interference and at the some time precludingthe leakage of light rays therethrough. The fingers 22 are individuallyadjustable by means of respective screws 26 the ends necked-down ofwhose shanks engage the bent bifuracted portions 27 at the ends of thefingers. The screws 26 engage threaded apertures in a supporting block28 which is in turn attached to the side wall of the scanner 10 byscrews 3 It will be evident that the above described arrangement permitseach finger to be moved in and out of the path of the light rays fromthe moving scanning spot S which impinge upon the lens system L and thatif the fingers 22 are adjusted so that the periphery of the resultingdiaphragm is fan-shaped as at A more light coming from the centerportion of the slot 12 will be blocked than rays coming from the endportions, i.e., the beam b1 from the ends of the slot will not bemodified appreciably. As shown in FIG. 9, the beam from the centralportions of the slot 12 will have a segment b2 of its light rays blockedwhereas the beam from the end portions of the slot is not appreciablymodified, so that the amount of light impinging upon the photoelectriccell from any position of the scanning spot along the slot 12 isadjustable by moving of the fingers 22 to be approximately the same, andthe electrical output of the cell for a uniform copy will be asindicated in the voltage-time diagram of FIG. 8.

It will be evident that although an adjustable diaphragm such asdescribed above has the advantage of permitting adjustments to be madeto compensate for the aging of photoelectric cells and for variationsbetween different photoelectric cells, it is also possible to obtainadequate compensation for the other factors causing variations in theamount of light reaching the photoelectric cell by substituting anoiradjustaele diaphraghm formed, for example, of a sheet of metalhaving a periphery shaped substantially similar to the outline of theends of the lingers 22 when in the position intlicatccl at A.

I claim:

1. The method of optically scunnin a subject copy in a facsimile systemcomprising the steps of feeding the copy lengthwise at a substantiallyconstant rate, illuminating successive transverse elements of the copyas it is led. scanning sequential incremental areas of theiilLllillllklllSLl transverse element to form a beam of light rays whichmoves in a plane passing through the scanned transverse clement,focussing the moving light beam to impinge upon a light sensitive deviceso that its output varies as a function of the copy contrast, andblocking a greater percentage of the light from the incremental areasdisposed centrally of the scanned transverse element than from theincremental areas adjacent either end thereof so that substantiallyconstant amounts of light impinge upon the light sensitive device fromall the incremental areas of a non-contrasting transverse element.

2. A mask for adjusting the iiitcnslly of light across an. optical path,comprising a plate, and a plurality of cylindrical elements carried bysaid plate and held hi:- iionally thereby, each 0) mid elements lacingimlcpemlcntly cxtemlalile info will path, the cleiilcllts in the platebeing arranged in rows with lhe elements 0, one row overlapping theelements of another row in said path.

3. A music for adjusting the intensity of light across an optical path,comprising a plate, and a plurality of elements carried by said plate(Hill held friciionally thereby, each 0] mid elements beingindependently extemlahie into said path, the elements lll ihe pit/rebeing arranged in rows with the elements of one row overlapping [heelements of another row in said path.

References Cited in the file of this patent or the original patentUNITED STATES PATENTS 1,807,0ll Ranger May 26, 1931 1,828,000 RangerOct. 20, 193i 2,094,318 Failla Sept. 28, 1937 2,298,911 Young Oct. 13,1942 2,4l0,550 Paclva Nov. 5, 1946 2,431,824 Poch Dec. 2, 1947 2,474,380Simmon June 28, 1949 2,528,020 Sunstein Oct. 31, 1950 2,557,691 RieberJune 19, 1951 2,672,799 Terwilliger Mar. 23, 1954 2929,87] Cross Ma 22,1960

